This is one of those charts which shows that, while numbers and statistics don't lie (over the long term, especially), there can be situations where they don't tell the whole story.

Since we are only looking at one month's sales, it's possible that July 2017 was a month where prices surged higher (high point), while July 2018 was a month where prices remained flat or even dipped (low point.) So we end up comparing a high point from one year with a low point from another year. (I'm only hypothesizing here, as I haven't yet run the month-by-month numbers to double-check..)

Last month's Chandler chart showed us the June comparison year over year, and the numbers showed long-term consistent growth. Obviously we'll have to take another look at Chandler's pricing soon...